The most complete summary! Read about TPU additives in one article!

The most comprehensive summary! Read aboutTPU additives​

Auxiliaries are important raw materials in the rubber industry. Although the dosage is small, the effect is huge. Polyurethane elastomers are inseparable from synthesis to processing and application. According to their different functions, they can be divided into synthetic systems, modified and There are four types of additives: operating system, vulcanization system and protective system.

Synthetic auxiliaries

01

Catalysts and polymerization inhibitors

In the synthesis of polyurethane elastomers, in order to speed up the main reaction, it is often necessary to add a catalyst. Commonly used catalysts include tertiary amines and organotin. Tertiary amines include triethylenediamine, triethylamine, and trimethylbenzyl. Amine, dimethylethanolamine, morpholine, etc., among which triethylenediamine is the most important; organotin types include stannous octoate, dibutyltin dilaurate, etc. In addition, there are organic mercury, copper, lead and iron, with organic lead and mercury being the most important, such as lead octoate and phenylmercuric acetate. Organic dibasic acids, such as adipic acid and azelaic acid, can be used as catalysts for polyether polyurethane casting rubber.

Amine catalysts are mostly used for foam-forming reactions in foam formulations. In polyether systems, amine and tin catalysts are used together to obtain the best cell structure.

Organotin catalysts usually catalyze the reaction process of HO and NCO, which can avoid the side reaction of OH. In addition to increasing the overall reaction rate, these catalysts can also increase the reaction activity of high molecular weight polyols and low molecular weight polyols. tend to be consistent, so that the prepared prepolymer has a narrower molecular weight distribution and lower viscosity.

The use of catalysts has a negative impact on the performance of the final elastomer product, mainly affecting high-temperature performance and hydrolysis resistance.

As polymerization inhibitors, acids and acid chlorides are commonly used. Acids use the most hydrogen chloride gas. Acid chlorides include benzoyl chloride, adipoyl chloride, etc.

02

Chain extenders and chain extender cross-linking agents

In the synthesis of polyurethane elastomers, chain extenders refer to diols and diamine compounds that are essential for chain growth reactions; chain extender cross-linking agents refer to compounds that both participate in chain growth reactions and Compounds that can form cross-linking points between chain segments, such as triols and tetrahydric alcohols, allyl ether diols, etc. Except for allyl ether glycol, which is not suitable for cast polyurethane elastomers, other chain extenders or chain extender cross-linking agents can be used. Thermoplastic polyurethane elastomers only use glycols; mixing polyurethane elastomers can use both glycols. Allyl ether glycols can also be used. Generally, low molecular weight aliphatic glycols and aromatic glycols can be used as chain extenders. Aliphatic glycols include ethylene glycol, butanediol and hexanediol, among which the most important one is 1,4-butane. Diol (BDO) is most commonly used in the preparation of thermoplastic polyurethane. It not only acts as a chain extender, but can also adjust the hardness of the product. Among aromatic diols, the most important one is hydroquinone dihydroxyethyl ether (HQEE), which can improve the rigidity and thermal stability of polyurethane elastomers; another aromatic diol is resorcinol Dihydroxyethyl ether (HER), which can maintain the durability, elasticity and plasticity of elastomers to the maximum extent, while limiting shrinkage to a minimum. Both HER and HQEE have the advantages of aromatic chain extenders and do not pollute the environment. However, when the use temperature drops slightly, HQEE has a tendency to crystallize rapidly, thus limiting its application. If HER and HQEE are mixed, this can be solved Crystallization problems can also improve the mechanical properties of products.

Generally used diamine chain extenders are aromatic, the most commonly used is 3,3′-dichloro-4,4′-diphenylmethanediamine (MOCA) chlorine on the benzene ring Atomic substituents reduce the reaction rate of amino groups with isocyanates, thereby extending kettle life, which is extremely important for hand-cast polyurethane elastomer products. Some other diamines, such as 3,3′-dichloro-polydiamine, 4,4′-diphenylmethanediamine, benzenediamine and triazinediamine, can also be used as polyurethane elastomers in the synthesis of Chain extenders, etc. Chain extender cross-linking agents include triols, tetraols and allyl ether glycols. Commonly used triols and tetraols include glycerol, trimethylolpropane, 1,2,6-hexanetriol and pentaerythritol. They react with isocyanates to form urethane cross-links; commonly used allyl ether glycol compounds are: α-allyl glyceryl ether (α-Age), trimethylolpropane allyl ether and glyceryl ether. Glyceryl allyl ether, the first two compounds can be added when synthesizing polyester, and allyl groups are introduced into the main chain of polyester; they can also be added when synthesizing raw rubber, and allyl groups are introduced into the main chain of raw rubber. In polyether production, all three compounds can be used.

Modifier operating aid

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05

Flame retardant

The flame retardant grade of materials is usually measured by the oxygen index: the oxygen index of first-level flame-retardant materials is >38, and the oxygen index of second-level flame-retardant materials is >25. The oxygen index of ordinary polyurethane elastic materials is 19-20, which is a flammable substance. When polyurethane is used in furniture, construction, automobiles, and paving materials, it must meet Class II or above flame retardant standards. Therefore, the application of flame retardants in polyurethane products is quite common, and it is the largest amount of compounding agent, accounting for about 1/3 of the total amount of compounding agents added to polyurethane. Flame retardants are divided into two categories: inorganic and organic. Inorganic flame retardants often contain aluminum, boron, zinc, antimony and other elements, such as aluminum hydroxide, hydrated alumina, borate, zinc oxide, antimony trioxide, etc. Their advantages It has good flame retardant effect, is cheap and does not produce smoke. The disadvantage is that it is solid and has high density, which puts higher requirements on metering, conveying and mixing equipment and is not convenient to use. Organic flame retardants often contain elements such as halogen and phosphorus. Among them, bromine-containing compounds have the best flame retardant effect. Chlorine-containing flame retardants produce greater smoke and toxicity when burned than phosphorus-containing flame retardants. The varieties with larger dosages include : Tris(2-chloroethyl)phosphate (TCEP) and tris(2-chloroisopropyl)phosphate (TCPP). In addition, there are triphenyl phosphate, polyamine phosphate, chlorinated paraffin, etc.

Various chemical additives occupy an important position in the field of fine chemicals. Although their dosage is not large, there are many varieties, wide uses, and high added value. Many companies at home and abroad are working hard to develop new ones. Types of additives, especially functional additives. Polyurethane is an emerging sunrise industry with excellent comprehensive properties and expanding application scope. However, in the trial production and production process of polyurethane elastic materials, domestic manufacturers currently do not widely use functional additives, and there is no urgent demand for adding additives to improve product performance. This shows that there is still a gap in understanding. Scientific research and trial production units should take the first step and use more cheap and high-quality new varieties of additives in polyurethane elastomers to contribute to accelerating the development of polyurethane elastic materials in my country.